CADMIUM HALIDE-COMPLEXES WITH PYRIDINE-N-OXIDE, AND THEIR CRYSTAL-STRUCTURES

Cadmium chloride and bromide form crystalline pyridine-N-oxide (pyo) complexes [{(CdCl2)3(pyo)2}n] (1) and an isomorphous pair [{CdX2(pyo)}n], X = Cl (2A), Br (2B). X-ray analysis of their structures shows them to have layer lattices arising from removal of a proportion of CdX2 units from the cadmium halide structures. There is retention of six-coordination through insertion of pyo bridges. The pyo rings overlie the voids created by removal of the cadmium centres. Complexes 2A and 2B have the chromium chloride connectivity. The cadmium iodide lattice is more readily degraded and a series of compounds having increasing pyo content is formed; viz [{CdI2(pyo)}n] (3) (an already known chain polymer). [{(CdI2)2(pyo)3}n] (4), [{CdI2(pyo)2}2] (5), and [Cd(pyo)6]2+ [CdI4]2- (6). Compound 4 is a chain polymer with mixed iodo- and oxo-bridges, and alternating five- and six-coordinated cadmium centres. Compound 5 is a pyo-bridged dimer with five-coordinate cadmium. In both 4 and 5 pyo plays both bridging and terminal roles. There is a methanolate derivative of 5, [{CdI2(pyo)2(MeOH)}2] (5A), with six-coordinate cadmium. The structures show the ease with which cadmium moves between five- and six-coordination, as well as the breaking of the Cd-I bond. In these structures cadmium shows no evidence of any disposition towards the strong diagonal bonding characteristic of mercury(II).